Processing information blocks for wireless transmission

ABSTRACT

In general, according to an embodiment, a wireless transmitter includes a plurality of coding and modulation modules to apply corresponding coding and modulation algorithms to input information blocks. A discrete Fourier transform (DFT) precoder applies DFT processing to outputs of the coding and modulation modules, and an inverse fast Fourier transform (IFFT) module receives a DFT output of the DFT precoder, which is mapped to different subcarriers according to the resource allocation indicated by the base station, and applies IFFT processing to the DFT output. An output processing stage produces output signals based on the output of the IFFT module to transmit wirelessly to a wireless receiver. In a different implementation, the outputs of the coding and modulation modules can be provided to an IFFT module to produce IFFT-processed output information.

BACKGROUND

Various wireless access technologies have been proposed or implementedto enable mobile stations to perform communications with other mobilestations or with wired terminals coupled to wired networks. Examples ofwireless access technologies include GSM (Global System for Mobilecommunications) and UMTS (Universal Mobile Telecommunications System)technologies, defined by the Third Generation Partnership Project(3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies,defined by 3GPP2.

As part of the continuing evolution of wireless access technologies toimprove spectral efficiency, to improve services, to lower costs, and soforth, new standards have been proposed. One such new standard is theLong Term Evolution (LTE) (also referred to as EUTRA (Evolved UniversalTerrestrial Radio Access)) standard from 3GPP, which seeks to enhancethe UMTS technology.

An issue associated with uplink wireless transmissions is powerconsumption associated with processing of information to be transmittedon the uplink. It is desired to achieve a low peak-to-average-powerratio (PAPR) to improve power efficient performance. However, in someimplementations, achieving the desired power efficient performance mayrequire use of relatively expensive power amplifiers in transmitters ofmobile stations due to large power amplifier backoff requirements. Poweramplifier backoff refers to operating the power amplifier at an outputpower level that is lower than the peak power level. A large poweramplifier backoff (lower average power level relative to the peak powerlevel) reduces the efficiency of the power amplifier.

Other goals associated with wireless transmission is wider bandwidth,higher spectral efficiency, and higher-order MIMO (multiple input,multiple output). MIMO refers to wireless transmission in which thetransmitter has multiple antennas and the receiver has multipleantennas, where multiple input means multiple transmitted signals intothe channel, whereas multiple output means multiple signals at theoutput of the channel. Conventional wireless transmitters may notprovide desired characteristics in an efficient manner.

SUMMARY

In general, according to an embodiment, a wireless transmitter includesa plurality of coding and modulation modules to apply correspondingcoding and modulation algorithms to input information blocks. A discreteFourier transform (DFT) precoder applies DFT processing to outputs ofthe coding and modulation modules. An inverse fast Fourier transform(IFFT) module receives a DFT output of the DFT precoder and applies IFFTprocessing to the DFT output. An output processing stage produces outputsignals based on an output of the IFFT module to transmit wirelessly toa wireless receiver.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are described with respect to thefollowing figures:

FIG. 1 is a block diagram of an example communications network thatincorporates an embodiment of the invention;

FIG. 2 is a block diagram of a wireless transmitter according to anembodiment;

FIG. 3 is a block diagram of a wireless transmitter according to anotherembodiment; and

FIG. 4 is a flow diagram of a process of processing information blocksfor wireless transmission, according to an embodiment.

DETAILED DESCRIPTION

In general, according to an embodiment, a more efficient technique ormechanism is provided for processing information blocks for wirelesstransmission over a wireless link between a wireless transmitter and awireless receiver. The technique or mechanism uses a wirelesstransmitter that has multiple coding and modulation modules to applycorresponding coding and modulation algorithms to input informationblocks. The modulation and coding algorithms can be different to allowfor link adaptation for subcarriers in different parts of a wirelesstransmission bandwidth between the wireless transmitter and wirelessreceiver. The wireless transmission bandwidth can include a number ofsubcarriers associated with corresponding different frequencies.

The wireless transmitter includes a discrete Fourier transform (DFT)precoder that applies DFT processing to outputs of the coding andmodulation modules. Note that one DFT precoder (rather than multiple DFTprecoders) is used to process the outputs of the multiple coding andmodulation modules. The use of just one DFT precoder to process outputsof multiple coding and modulation modules allows for a more efficientimplementation.

An inverse fast Fourier transform (IFFT) module receives a DFT output ofthe DFT precoder and applies IFFT processing to the DFT output. Anoutput processing stage then produces output signals based on an outputof the IFFT module for transmission wirelessly to a wireless receiver.

In accordance with some embodiments, the DFT output of the DFT precoderis mapped to an input of the IFFT module as clusters of contiguoussubcarriers (having respective different frequencies). The clustering ofsubcarriers allows for improvement in the PAPR (peak-to-average-powerratio). Also, such an embodiment provides for an improved cubic metric(CM), which is the metric used to estimate the reduction in powercapability of a power amplifier in a wireless transmitter.

In accordance with some embodiments, the information block processing isapplied to uplink wireless transmission (from a mobile station to a basestation). However, even though reference is made to application of theinformation block processing in the uplink direction, note that in otherembodiments, the information block processing can be applied in thedownlink direction as well.

As used here, an “information block” refers to a collection ofinformation bits, which can represent traffic data or control signaling.A “mobile station” refers to a terminal accessible by a user and that isable to move from location to location. A “base station” is a wirelessaccess network entity that is responsible for wireless communicationswith a mobile station. A base station can include a base transceiverstation (BTS) and a base station controller or radio network controller,for example.

FIG. 1 illustrates a communications network that includes a base station100 that is able to communicate with a mobile station 102 over awireless link 104. The base station 100 and mobile station 102 are eachconsidered a wireless communications device. The base station 100 ispart of a wireless access network, which can include many base stationsto provide coverage for respective coverage areas (cells). Each basestation 100 can communicate with multiple mobile stations within thecoverage area of the base station.

The base station 100 is in turn connected to a core network 106associated with the wireless access network. The core network 106includes nodes, such as gateway nodes, to interface the wireless accessnetwork to an external network 108, which can be an external datanetwork (e.g., Internet).

The core network 106 and wireless access network including the basestations 100 can operate according to one of various differenttechnologies, including as examples: GSM (Global System for Mobilecommunications) or UMTS (Universal Mobile Telecommunications System)technology, defined by the Third Generation Partnership Project (3GPP);CDMA 2000 (Code Division Multiple Access 2000) technology, defined by3GPP2; Long Term Evolution (LTE) technology or EUTRA (Evolved UniversalTerrestrial Radio Access) from 3GPP, which is an enhancement of the UMTStechnology; WiMax (Worldwide Interoperability for Microwave Access)technology, as defined by IEEE (Institute of Electrical and ElectronicsEngineers) 802.16 standards; and other technologies.

The base station 100 includes a transmitter 110 and a receiver 112, andthe mobile station 102 includes a transmitter 114 and receiver 116. Thetransmitter 110 in the base station 100 is used to transmit downlinkinformation through an antenna assembly 118 of the base station 100 overthe wireless link 104. The downlink information is received by thereceiver 116 of the mobile station 102 through an antenna assembly 120of the mobile station 102.

In the other direction, uplink information is transmitted by thetransmitter 114 in the mobile station 102 through the mobile stationantenna assembly 120 over the wireless link 104. The uplink informationis received by the receiver 112 in the base station 100 through the basestation antenna assembly 118.

The base station 100 further includes a processor 122, and the mobilestation 102 includes a processor 124. The processors 122 and 124 controlrespective tasks performed by the base station 100 and mobile station102, respectively, including transmission and reception of informationover the wireless link 104. For example, a processor can provideinformation (traffic data or control signaling) to a respectivetransmitter for transmission over the wireless link 104. The processorcan also process received data that has been received by thecorresponding receiver over the wireless link 104.

FIG. 2 illustrates components of a transmitter (e.g., 110 or 114 in FIG.1), according to an embodiment. The transmitter includes multiple codingand modulation modules 202_1 to 202_N that receives input information200 (in the form of input information blocks). The output of each codingand modulation module includes a group of coded and modulated symbols,represented as 203 _(—) i, where i=1−N. The group of coded and modulatedsymbols 203 _(—) i is output from a corresponding coding and modulationmodule 202 _(—) i. Each group of coded and modulated symbols 203 _(—) iis provided to a corresponding different part of a DFT precoder 204,where each corresponding part of the DFT precoder 204 applies DFTprocessing on the respective group of coded and modulated symbols 203_(—) i. A single DFT precoder provides for improved (reduced) peak toaverage power ratio of the transmit signal at the IFFT output, ascompared to the case when multiple DFT precoders are used, where the DFTspreading is across a bandwidth equivalent to the number of modulationsymbols for the individual code block. In the case of a single DFTprecoder, all the modulation symbols in the time-domain are spreadacross a bandwidth that is equivalent to the total allocated bandwidthfor the mobile station in the uplink, which is more effective inreducing the peak to average power ratio.

The DFT precoder 204 outputs multiple clusters 205_1 through 205_N ofsubcarriers. Each cluster 205 _(—) i of subcarriers contains aDFT-processed version of the corresponding input group of coded andmodulated symbols 203 _(—) i. The arrangement used in FIG. 2 allows forthe DFT output to be mapped to the IFFT input (of an IFFT module 206) asclusters of contiguous subcarriers; this clustering of subcarriersallows for improvement in PAPR and CM characteristics.

The IFFT module 206 applies inverse fast Fourier transform processing onrespective input clusters 205_1 to 205 _(—) n. The mapping of theclusters to the input of the IFFT module 206 is based on the resourceallocation corresponding to the mobile station's transmission.Basically, different parts of the IFFT module 206 are used to processcorresponding clusters 205_1 to 205_N. The IFFT-processed information isthen output to an output processing stage 208, which performs variousprocessing including parallel to serial conversion, cyclic prefixinsertion, windowing, carrier modulation, filtering, frequencyup-conversion and power amplification to output analog RF signals thatare to be wirelessly transmitted by the antenna assembly 118 (in thedownlink direction) or 120 (in the uplink direction).

The wireless transmitter arrangement shown in FIG. 2 is considered aclustered DFTS-FDMA (discrete Fourier transform spread-frequencydivision multiple access) arrangement.

In an alternative embodiment, for uplink wireless transmission, atransmitter (e.g., 120 in FIG. 1) containing components of FIG. 3 can beemployed. Input information 300 (in the form of input informationblocks) is provided to corresponding coding and modulation modules 302_1to 302_N, which can apply different coding and modulation algorithms torespective input information blocks. The output of each coding andmodulation module 302 _(—) i is a corresponding group 303 _(—) i ofsymbols that are provided to an IFFT module 304. After applying IFFTprocessing, the output of the IFFT module 304 is provided to an outputprocessing stage 306, which performs processing to produce signals foruplink transmission by the antenna assembly 120.

The arrangement shown in FIG. 3 is an OFDMA (orthogonal frequencydivision multiple access) arrangement that provides more flexible uplinkmultiple access with lower complexity as compared to the transmitterdepicted in FIG. 2. Specifically, using OFDMA, the DFT precoder 204 doesnot have to be used. OFDMA provides a relatively large number ofclosely-spaced orthogonal subcarriers (of different frequencies) forcarrying information. OFDMA also defines time slots (along a timedimension). By providing multiplexing in both the time dimension andfrequency dimension, subbands can be provided, where each subbandincludes a number of subcarriers along the frequency dimension and timeslots along the time dimension.

FIG. 4 is a flow diagram of a process of processing input informationblocks according to an embodiment. The processing is performed bycomponents of a transmitter. Input information blocks are received (at402). The received information blocks can include traffic data orcontrol signaling. By applying different coding and modulationalgorithms to different information blocks, link adaptation can beperformed for different parts of the transmission spectrum to improvecommunications reliability and spectral efficiency. For example, certainparts of the transmission spectrum may be associated with poor channelconditions, such that a more robust coding and modulation algorithmshould be applied to improve reliability and performance.

Selection of coding and modulation to be applied can be based onscheduling performed at the base station using feedback information fromthe mobile station, where the feedback information includes CQI (channelquality indicator) and/or PMI (precoding matrix index). PMI refers to anindex (or other type of indicator) to enable selection of a precodingvector to be applied to wireless transmissions. CQI is an indication ofwireless channel quality between the base station and the mobilestation. Different values of PMI select different codewords or precodingmatrix. Based on the feedback information provided from the mobilestation to the base station, the base station can schedule the mobilestation to apply selected coding and modulation algorithms to respectiveinformation blocks at the coding and modulation modules (202_1 to 202_Nor 302_1 to 302_N). The scheduling by the base station is accomplishedby the base station sending control messages containing indications ofcoding and modulation algorithms to apply by the respective coding andmodulation modules. Coding here may include channel coding, e.g.,convolutional or turbo encoding, interleaving and rate matching stages,as in the case of LTE.

Next, the coded and modulated symbols are output (at 406) by the codingand modulation modules (202_1 to 202_N or 302_1 to 302_N) for furtherprocessing to produce output signals. The further processing can includeprocessing by a DFT precoder 204, the IFFT module 206, and outputprocessing stage 208 (FIG. 2), or by the IFFT module 304 and outputprocessing stage 306 (FIG. 3).

The output signals are then wirelessly transmitted (at 408) by anantenna, such as antenna 118 or 120 in FIG. 1.

The various modules depicted in FIG. 2 and FIG. 3 can be implementedwith hardware only, or implemented with a combination of hardware andsoftware. Thus, the coding and modulation module can be implemented withhardware only or hardware and software, the DFT precoder can beimplemented with hardware only or hardware and software, and the IFFTmodule can be implemented with hardware only or hardware and software.

In the foregoing description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details. While the invention has been disclosedwith respect to a limited number of embodiments, those skilled in theart will appreciate numerous modifications and variations therefrom. Itis intended that the appended claims cover such modifications andvariations as fall within the true spirit and scope of the invention.

1. A wireless transmitter comprising: a plurality of coding andmodulation modules to apply corresponding coding and modulationalgorithms to input information blocks; a discrete Fourier transform(DFT) precoder to apply DFT processing to outputs of the plurality ofcoding and modulation modules; an inverse fast Fourier transform (IFFT)module to receive a DFT output of the DFT precoder and to apply IFFTprocessing to the DFT output; and an output processing stage to produceoutput signals based on an output of the IFFT module to transmitwirelessly to a wireless receiver.
 2. The wireless transmitter of claim1, wherein the DFT output is mapped to an input of the IFFT module asclusters of contiguous subcarriers.
 3. The wireless transmitter of claim1, wherein the coding and modulation algorithms applied by the pluralityof coding and modulation modules enable link adaptation for subcarriersin different parts of a wireless transmission spectrum.
 4. The wirelesstransmitter of claim 3, wherein at least two of the coding andmodulation algorithms are different.
 5. The wireless transmitter ofclaim 1, wherein the coding and modulation algorithms to apply by therespective coding and modulation modules are scheduled by a basestation.
 6. The wireless transmitter of claim 5, wherein the coding andmodulation algorithms to be applied by the coding and modulation modulesare based on control indications received from the base station at amobile station containing the wireless transmitter.
 7. A mobile stationcomprising: a wireless transmitter for wirelessly sending signals to awireless receiver, wherein the wireless transmitter includes: aplurality of coding and modulation modules to apply respective codingand modulation algorithms to respective input information blocks; aninverse fast Fourier transform (IFFT) module to receive outputs of theplurality of coding and modulation modules and to produce IFFT-processedoutput information based on the outputs of the plurality of coding andmodulation modules; and an output processing stage to produce outputsignals for wireless transmission based on the output information of theIFFT module.
 8. The mobile station of claim 7, further comprising aprocessor to produce information to be transmitted by the wirelesstransmitter.
 9. The mobile station of claim 7, wherein selection ofcoding and modulation algorithms to apply is based on controlinformation from a base station.
 10. The mobile station of claim 9,wherein the control information from the base station is based on anestimate of uplink channel quality.
 11. The mobile station of claim 7,wherein an arrangement including the plurality of coding and modulationmodules and the IFFT module provides OFDMA (orthogonal frequencydivision multiple access) communications.
 12. The mobile station ofclaim 7, wherein the mobile station is configured to communicatewirelessly according to an Evolved Universal Terrestrial Radio Access(EUTRA) standard.
 13. A method of wirelessly transmitting informationblocks, comprising: applying, by a wireless transmitter, plural codingand modulation algorithms by respective coding and modulation modules tothe information blocks; providing coded and modulated information to adiscrete Fourier transform (DFT) precoder in the wireless transmitter toapply DFT processing to the coded and modulated information from thecoding and modulation modules; applying, by an inverse fast Fouriertransform (IFFT) module in the wireless transmitter, IFFT processing ona DFT output of the DFT precoder to produce an IFFT-processed outputfrom the IFFT module; and producing output signals based on theIFFT-processed output for transmission wirelessly to a wirelessreceiver.
 14. The method of claim 13, wherein the DFT output is mappedto an input of the IFFT module as clusters of contiguous subcarriershaving corresponding different frequencies.
 15. The method of claim 13,wherein at least two of the coding and modulation algorithms aredifferent.
 16. The method of claim 13, wherein wireless communication bythe wireless transmitter is according to an Evolved UniversalTerrestrial Radio Access (EUTRA) standard.
 17. A method of wirelesslytransmitting information blocks, comprising: applying coding andmodulation algorithms by respective coding and modulation modules of awireless transmitter to respective information blocks, wherein thewireless transmitter is part of a mobile station; receiving outputs ofthe coding and modulation modules at an inverse fast Fourier transform(IFFT) module; producing by the IFFT module, IFFT processed outputinformation based on the outputs of the coding and modulation modules;and producing output signals for wireless transmission in an uplinkdirection based on the IFFT-processed output information from the IFFTmodule.
 18. The method of claim 17, further comprising: receivingdownlink control information from a base station, wherein selection ofcoding and modulation algorithms to apply by the coding and modulationmodules is based on the control information.
 19. The method of claim 18,wherein the control information is based on feedback from the mobilestation to the base station.